Preparation of polyvinyl acetate emulsions



Patented Oct. 14, 1952 UNITED vSTATES PATENT OFFICE ;,,2,614,0s v H PREPARATION OF POL VINYL ACETATE EMULSIONS Y Norris IslandiN. assignor to 11.; I. du Pont; fie Nemours andfiompany, Wilmington, DeL, a corporation of Delaware No'Dr-awiiig. ApplicationAugust 12,1950;

7 serial No. 179,093

p .This invention relates. o...the.eniulsion.;,polymerization .ofyinylacetate and moreparticularly to the preparation of annimprovedaqu'eous dis- I persion of polyvinylacetate.

. .Stable. aqueous dispersions of polyvinyl. acetate ordinarily, called. (polyvinyl acetate emulsions are commonly made. .by dispersing .monomeric acetate. emulsions-are. us ful; r. a

. variety of. purposes, includin ,adhesive and coatins. u es... -fiihe. .emu1sions,,.wh en sprea ;,u cn a solid surface and permitted to dry,;;for m epntinucusfilms wh eharepz te ;tr nsp ren 4811011 films :sp ead betwee two. s id.;=hgd1es irlinerm tt d to...d y .thererfermnn excel en adh iv be d... Fo .suehcwfinsand adh s Ji sath smay hemmed wit @th e s edi t solid or liquid, to serve as fillers, pigments, reinforcing agents, extenders, plasticizers and solnt For x m l bye i e leeddii ee Qfin.\vater -'b"asepaint forinulat onsl' In the uses of the polyvinyl a'cet as coatings andaclhesives, difiiculti hayeari'sen because of the lack' of adequate Water resistance. The. presence of the. dispersing; agent utilized in making the emulsion; remainly, sp'Q'n'sible for the lack'ofvvatef resistance inlfilin s'obtaind'trom the emulsion The dispefsing agent ten v,td cause .the redispersion .of the polymersthus imparting to. the' films the efie'ct of water solubility toagreater or 1855 extent. .v ,7 Various methods haveib'een propb sedhe'retofore for reducing" theivater sensitivity of films'pbmerits and solvents, the emulsionsniay be. utilized tained froml polyvinyl acetate emulsions. one

edpis e? th fil dur n 9? a ter its formationwith a substance which chemically reacts. with the dispersing agent to destroy its effectiveness as a dispersing agent. In ,manyremulsions which utilize .water solublegradesof polyvinyl alcohol .asdispersing agents, water sensitivity can be reduced more orless by treating the emulsion duringo'r after a coating process" With a emits; (01. 2604 applying the vinyl resin tdtextile andlbai er material such as -an aldehydeorthe: lk wh'h will insolubilize the polyvinyl alcohol, therebyflestroying its 'dispersingactivity. Such have the disadvantage. ofrequiring a operational steps such as treating the coated articlesor mixing ina treating agent just prio to application ofthe vinyl resin emulsion. .Anqther method comprises adding to the vinyl reslnemulsion materials capable Of -ins IubiliZingthe pc vin alcohol r oth r. i per nea t l i s a ans; beeee e v u successful .forthe reason that gener agents tendto react with the dis while the emulsion is instorage or, sh causing coagulation. It f u e e b e: 01? A t V which can bestored and shipped for ind periods of time without coagulation"and wh ch. when spread intoa film-and dried attem'pfef atures of 201m 25 C. or higher, forma does not redisperse when contacted with ter.

For many uses ofthe polyvinyl acetate sions. high dilution stability is. a ,very. de Sl able property. ,In 4 many applications, ,for. examine; in

lyt note it is desired to dilute theemulsibfn. with to as low as. 1. to.3 .%Vpolyr ner concentration 'erally, it is" not possible,to,.dilute polyvinyl acetate emulsions to a polymersc ontentlof .les'sthan I about .30% ,,as at lower-concentrations the emulsion becomes .unstableand tliei virnil, resin articles tend .to coagulate onsettle. out tonan eikces'siveextentu Consequently for applicati' grequiring highdilutions, it has ben -necess'ary to add a protective colloid or thickeninggagentor to cofiirliinuously agitate the diluted emulsion; or An object of this invention is an improved process for the production of polyvinyl acetate I j are, lr' yvinyl acetate emulsion, stable during storag'e and shipment, from which substantially. completely Water-resistant f lms can be, cast Without the necessity of chemical or heat treatments;

- other object is to prepare a polyvinyl' acetate emulsion having ahigh dilution fisitability. Still other objects r the invention will beappa'rnt from the following description.

I The above objects may be attainedin accordance withthe present invention by the herein described method'for polymerizing vinyl" acetate. l'his method depends upon the use-ore completely hydrolyzed gradebf' polyvinylalcohol (or certain other polyhydroxy polymeric film-forming substance hereinafter -described)sas --the-dispersing agent, the utiliz'ation'of a certain tech- 3 nique in carrying out the polymerization and the presence, during at least a part of the polymerization reaction, of a small amount of a long-chain, primary, monohydric aliphatic alcohol containing 8 to 20 carbon atoms per molecule.

In one method for polymerizing vinyl acetate in accordance with my invention, I may first dissolve a completely hydrolyzed grade of polyvinyl alcohol in hot water to form a solution containing from 4.5 to 6% by weight of the polyvinyl alcohol. I then add a small amount of vinyl acetate not exceeding 1.5 to 3% of the weight of the aqueous solution and disperse this by adequate agitation. Polymerization catalyst is then added and the dispersion, with continued agitation, is brought to a suitable temperature, for example, 82 to 90 C. so as to cause polymerization of the dispersed vinyl acetate. At any time after the polymerization reaction has started, including a time sufilcient to completely polymerize the initial quantity of vinyl acetate, further small quantities of vinyl acetate are added, either continuously or intermittently, provided that the amount of vinyl acetate added or the rate of addition of vinyl acetate is such that the amount of vinyl acetate in the reaction mixture never exceeds 5% of the weight of the aqueous portion,

' so long as the amount of polymer formed does not exceed 20% of the weight of said aqueous portion. When the amount of polymer formed has increased to more than 20 by weight of the aqueous portion, the addition of the vinyl acetate monomer may be increased, if desired, so long as it is then not permitted to exceed 3 by weight of the aqueous portion. The process is continued until the desired amount of polymer formed has reached 30 to 40% by weight of the mixture. As the polymerization progresses, further amounts of catalyst may be added, as required to maintain a suitable catalyst concentration.

The pH of the reaction mixture must be controlled and at the start of the reaction mixture must be above 4, e. g., at a pH of 6 to 8. During the reaction the pH will fall, due to some hydrolysis of vinyl acetate to form acetic acid. At

' completion of the polymerization the pH will be less than 6, e. g., around 3 to 4.

Before or during the polymerization reaction I add to the reaction mixture a small amount of a high molecular weight, primary, monohydric alcohol, for example, lauryl alcohol in amount equal to 0.1 to 1% by weight of the water present.

V the total that is to be polymerized. For example,

if the completed polyvinyl acetate emulsion is to contain 50% by weight of polyvinyl acetate,

the polymerization is considered 50% complete when half of the required amount of vinyl acetate has been polymerized, that is, when the polymer concentration reaches about 33%. However, the time at which the high molecular weight alcohol is added to the reaction mixture will depend upon the properties desired in the resulting emulsion. By adding the alcohol before the polymerization starts, I obtain a vinyl resin dispersion having exceedingly small particles and having high dilution stability. Emulsions made by this method generally can be diluted down to a polymer concentration of as low as 1 to 3% by weight with little or no loss of stability. On the other hand, if the alcohol is added when the polymerization is from 20 to 50% complete, the dilution stability is not quite as high, but the resulting emulsion will have a greater affinity for cotton and hence better suited for certain uses in coating cotton fabrics. More specifically, when cotton cloth is coated or impregnated with such emulsions, dried and then heat treated, e. g., by ironing, the dried polymer serves as a so-called permanent starch," which is not removed by repeated laundering of the fabric. If the high molecular weight alcohol is added at the start of polymerization or before polymerization is 20% complete, when used as a permanent starch, the polymer is less resistant to repeated laundering.

The amount of the high molecular weight alcohol such as lauryl alcohol may vary from about 0.1 to as high as about 5% of the weight of polyvinyl acetate in the finished emulsion. Preferably this proportion will not exceed 1%, as with higher proportions the resultant emulsion tends to have poor wetting properties. Also large amounts of the high molecular weight alcohol tend to inhibit polymerization to some extent. These deleterious effects of excess alcohol are not very great at proportions up to 5%.

The resulting polyvinyl acetate dispersions are latex-like or creamy compositions which yield clear, transparent, substantially water insoluble films of vinyl acetate when spread on solid surfaces and dried at temperatures of 20 to 25 C. or higher.

I have found that such non-redispersible filmforming emulsions cannot be made (1) by using a partially hydrolyzed grade of polyvinyl alcohol as the emulsifying agent, regardless of the rate of monomer addition nor (2) by using a completely hydrolyzed grade of polyvinyl alcohol as emulsifier when the rate of monomer addition during polymerization is not maintained as described above.

The invention is further illustrated by the following examples. In these examples the properties of the polyvinyl emulsions noted were determined by the following characterization procedures, except as otherwise indicated.

Characterization procedures Particle size.The particle size of the emulsion is determined by examination of a highly diluted sample under a microscope equipped with a calibrated scale.

pH.Beckmann pH meter (measured at 25 C.).

Viscosity.-The viscosity is determined at 25 C. with a Brookfield viscosimeter, with the spindle rotating at 60 R. P. M. and reported in centipoises (cp.).

Air-dried fiZm.A 0.008" thick wet film is cast on a 7%" x 17" ground glass plate with a Boston Bradley adjustable blade doctor knife. It is placed in a constant temperature room at 72 F. and 72% relative humidity for 24 hours. This film is used for observation of clarity, redispersion and number of oscillations-wet rubs.

Redispersion.-Redispersion is noted when the above film is wet with water and rubbed with a nylon brush; if the water becomes milky, redispersion is stated to occur.

Number of oscillations-wet rubs.--The aboveindicated air-dried film is tested according to the Federal Specifications TTP-88a (with the modification that water instead of soap solution is used and no "heat treatment of film is permitted) with a Gardner Model 105 washability and abrasion machine. In this testthe film is scrubbed with a wet-weighted nylon brush. The number of oscillations of this wet scrubbing is noted when any area of theeentral 4"- section of the film fails. A test .of-dOOO oscillations or better indicates excellent "wet abrasion resistance. The designationfO: K. indicates no observable failure of the film.

Per cent screen-ies'tF-A loll-gram sample or" the emulsion is diluted with water to 1000 grams and is run through a weighed-Zlidrrieshper sir-in; screen. The screen is washed until the filtrate is clear. It is then dried in the oven to constant weight. An emulsion of 0.1% or less screen test on 200 mesh 'screen is acceptable to most users of polyvinyl acetate emulsions; In many applications, an emulsion with a screen test of 02% or greatei would -have to be screened before use 6% solids dilu'tzo'n settling testP-The polyvinyl acetate emulsion'is diluted with water to 6% solids and 100cc. of the diluted emulsion is allowed to stand for -24 hours.' -A -rea"ding is taken of the number of cc. of sludge settled out. (This is an indication of dilution stability. An emulsion of less than 2 cc; can be used by" most emulsion consumers who apply, the emulsion in a dilute form. An emulsion which contains more than 3 cc. of sludge in 100 cc of 6% solids would be unsatisfactory for dilute application.)

The polyvinyl alcohol and NaHCOz were stirred into the water in a reactorfitted with a sealed stirrer, reflux condenser, thermometer well and thermometer, and graduates for addition of catalyst (H202) and sulfoxylate. This mixture was cooked for one hour at about 90 C. 23 grams of vinyl acetate was added and thereafter, with continuous agitation, H202, the sulfoxylate and vinyl acetate were added at a rate which maintained a steady polymerization and so as to maintain the monomer content below 3% by weight. The polymerization temperature was maintained at'87" to 90 C. The polymerization time was two hours and eighteen f6% solids dilution settling I test 1.5 cc.

f6 EX A m in 2 M'rii'iiiils Water Completely hydrolyzed graceof polyvinyl 'a'lcohol 105.3 g'r Nanooi 255 gr Lauryl alcohol ."11.2"gr. Vinyl acetate 1472 gr. Zinc formaldehyde sulfh lgnrylaixe"(6%) 32.2 cc. H502 (4%) 322 CC.'

Pat/memorize The polymerization w -carried 'oiitfiiithe same reactor andunder the 's amebon'ditions indicated for Example 1 except for the use "of lauryl alcohol to improve parade size} The 'lauryl alcoholwas added to the cookedsoliition of polyvinyl alcohol before'starti-ng-the polymerization. The polymerization temperature was maintained at 87? to 90 The time required for polymerization was two-'hours' an'd twenty-five minutes. The emulsion-was cooled to room'temperature with 'mocl'eratestirri'fig [The polymerization was carried out ,iwlth'the above materials in the samereactor and under the same conditions as indicated in Example2. The polymerization temperature was maintained at 86 to 91. The polymerization time was one hour and twenty minutes. The finished emulsion was cooled to room temperature with moderate stirring.

Characterization Particle size: r l I v,

Predominant spheres 0.5'micron Range spheres Q.5t66'. rhierons Agglomer'ates uptd I2mi'crons pI-I Air-dried film- '04--. Clear Redispersion None Percent en has 9.34%; 6% solids dilution settling test 1.0 cc.

7 EXAMPLE 4 Materials Water 1109 lbs. Completely hydrolyzed grade of polyvinyl alcohol 58 lbs., 5 oz.

NaHCOs 1 lb., 6 oz. Lauryl alcohol 6 lbs., 8 oz. Vinyl acetate 815 lbs. Zinc formaldehyde sulfoxylate (8%) 24,200 cc. Hydrogen peroxide (4%) 20,900 cc.

Polymerization The polymerization was carried out in a 300 gallon jacketed Monel vessel fitted with an agitator, reflux condenser and flow-meters for the sulfoxylate and H202. The polyvinyl alcohol was slurried in the (cold) water charge and the sodium bicarbonate and lauryl alcohol were added. The mixture was cooked at 80 to 90 C. for about two hours. About 15 lbs. of vinyl acetate was added to displace air and establish a mild reflux. Vinyl acetate, H202 and sulfoxylate were added over a period of 4.3 hours. The maximum monomeric vinyl acetate content was 2.3%. The reactor was maintained at 86 to 89 C. during most of the run. The vinyl acetate content was reduced to 0.5% by steaming and the emulsion was cooled in another vessel made of stainless steel.

Characterization Particle size:

Predominant spheres 0.5 micron Range spheres 0.2 to 5 microns Agglomerates few up to ca. 20 microns pH 4.5 Viscosity 50 cp. Air-dried film Clear and smooth Redispersion None Percent screen test 0.02% 6% solids solution settling test 0.5 cc.

EXAMPLE 5 Materials Water 1000 cc. Completely hydrolyzed grade of polyvinyl alcohol 52.6 gr. NaHCQ; 1.275 gr.

"Lorol-5 (A commercial product containing about 90% of lauryl alcohol) 5.6 gr.

Vinyl acetate 736 gr.

Sodium formaldehyde sulfoxylate (6%) 23.5 cc.

H202 (4%) 23.5 cc.

Polymerization The polymerization was carried out as indicated in Example 2 except that the Lorol-5 was dissolved in the vinyl acetate. The polymerization mixture was maintained at 86 to 93 C. The polymerization time was two hours and twenty-five minutes.

Characterization Particle size:

Predominant'spheres ca. 0.1 micron Range spheres 0.1 to 3 microns Agglomerates up to ca. 20 microns pH 4.45 Viscosity 760 cp Air-dried film Clear Redispersion None Percent screen test 0.05% 6% solids dilution settling test 0.5 cc.

8 EXAMPLE 6 Materials Water 1000 cc. Completely hydrolyzed grade of polyvinyl alcohol 52.6 gr.

NaHCOa 1.275 gr. "Lorol-5 5.6 gr. Vinyl acetate 736 gr. Zinc formaldehyde sulfoxylate (6%) 25.3 cc. H202 (4%) 25.5 cc.

Polymerization The procedure was the same as in Example 5, but at a temperature of to C. The polymerization time was two hours and twenty-five minutes.

Characterization Particle size:

Predominant spheres Ca. 0.1 micron Range spheres 0.1 to ca. 2 microns Agglomerates up to 10.0 microns pH 4.95 Viscosity 580 cp, Air-dried film Clea Redispersion None Percent screen test 0.039% 6% solids dilution settling test 0.7 cc.

The polyvinyl alcohols suitable as emulsifiers in practicing my invention are those which are made by reacting polyvinyl acetate with an alcohol or water until at least 98% of the acetate groups have been converted to hydroxyl groups. I prefer to use polyvinyl alcohols which are thus 99 to 100% saponifled. Such polyvinyl alcohols are herein and in the appended claims termed "completely hydrolyzed grade of polyvinyl alcohol.

The above described completely hydrolyzed grade of polyvinyl alcohol as generally made is insoluble or only slightly soluble in cold water, 1. e., at temperatures below 50 C.; and in order to prepare an aqueous solution thereof for the practice of this invention I usually stir a mixture of water and the polyvinyl alcohol at a temperature above 50 C. until a substantially clear solution is found. Preferably, I stir the mixture to disperse the polyvinyl alcohol (in finely divided form) in the water and heat the dispersion at 80 to C. for about one hour, to obtain a clear solution. Such solution may be cooled to room temperature, without precipitation of dissolved polyvinyl alcohol.

Certain polyhydroxy polymeric film-forming substances other than the completely hydrolyzed grades of polyvinyl alcohol may also be used as dispersing agents in my process, for example, certain starches and hydroxy alkyl celluloses. To serve as a substitute for completely hydrolyzed grades of polyvinyl alcohol in this process, the polymeric material must contain hydroxyl groups in proportions equal to or greater than that of other functional groups (such as ether groups, ester groups, carboxyl. sulfonyl and the like) and must also have substantially the water solubility characteristics described above. That is, it must be substantially insoluble or only slightly soluble in water at temperatures below 50 C. but soluble when heated with water at temperatures at or above 50 C. (e. g., 70 to 0.), to form solutrons. One example is any of the various known soluble starches, which must be heated to 70 or higher in contact with water to form aqueous solutions. Such soluble starch, suitable for my purpose, may be made, for example, by partially sulfonating starch, so that less than half of the hydroxyl group of the starch are sulionated. Otherforms of modified starch containing a preponderance of free hydroxyl groups and having the above solubility characteristics may be used as well.

The hydroxy alkyl celluloses (hydroxy alkyl.

cellulose others) which have the above described solubility characteristics, e. g., hydroxy ethylcellulose, also may be used in place of the. completely hydrolyzed grades of polyvinyl alcohol topractice my invention.

The concentration of dispersing agent in the polymerization reaction mixture will vary, depending onits dispersing power and theviscosity of its, aqueous solution. For example, a com pletely hydrolyzed grade of polyvinyl alcohol, a 41% by weight aqueous solution. of which. hasa viscosity less than 100 centipoises at20 C., will. be. employed as a 4.5 to 6% byweightadueoussolution; 10%, may be employed if desired. Other. completely hydrolyzed grades of polyvinyl. alcohol. whose aqueous solutions have higher viscosities. may be used in lower concentrations, e. g., around.- 2.%. In general the concentrations of dispersing agent in the practice ofv my invention does not depart from conventional. practice in emulsion polymerization of vinyl acetate, sufficient dispersing agent being employed to form; a stable dispersion of the resulting polymer.

The catalyst preferably used. in my process is the type I term activated peroxide type polymerization catalyst, by which term I. mean the combination of a peroxygen compound anda reducing agent, for example, a bisulfite, suliurous acid, sulfoxylate or other sulioxy compound having reducing properties. The peroxygen com pound may be hydrogen peroxide, an organic peroxide such as benzoyl peroxide, acetyl peroxide or the like, an organic or inorganic peracid or a salt thereof, e. g., peracetic acid, perborates and persulfates. The best results generally are ob tained by using a Water soluble peroxygen com.- pound, e. g., hydrogen peroxide or an inorganic persulfate or perborate. Also I generally prefer to add. the peroxygen compound and the. reducing compound separately to the polymerization reaction mixture. A preferred catalyst is. the. combination of hydrogen peroxide with. a sulfoxylate, e. g., zinc formaldehyde sulfoxylate separately added. Such activated peroxygen type polymerization catalysts are well. known in the art and. are described, for example, in Brubaker et al., U. S. P. 2,462,354. While I prefer to utilize.

the above activated peroxide? type of catalyst, the invention is not restricted thereto, as other catalyst suitable for the polymerization. of vinyl acetatev may be. used, for. example, any. of the.

various peroxygen compoundssuch as thosementioned above, with or withoutthe, addition of reducingagents. or other activatingmaterials and.

the various azo compounds which have been more recently discovered to catalyze vinyl acetate polymerization.

The amount of catalyst and the temperature of the reaction mixture during the polymerizationare not critical and may follow conventional procedures for the; polymerization of vinyl acetate. I generally prefer to add the catalyst in smalllamounts simultaneously with the addition of the monomer, but such is not essential, so long as. the catalyst concentration is maintained s fliciently high to cause polymerization.

Still higher concentrationa. eg., 6.130.

. than one olefinic group -CI-I: CH.

20 25" C. form, films highly resistantto redispersion in water it", is essential that :v

(1) The dispersing agent be either a completely hydrolyzed grade 'ofi-polyvinyl alcohol as defined above or other. polyhydroxy polymeric substance in which free hydroxyl, groups are present in amount equal to or greater than other functional groups and which is soluble in water at a temperature above 5.0.? 0.. but" insoluble in water at temperatures below50? C.

(2) The amount of, monomeric vinyl acetate present in the reaction mixture does not exceed 5% of the weight of thewater-present when the polymer content. ofithe emulsion is: 20%- by weight or less, and does notexceed. 3% of the weight of the water whenthe polymer content is above 20% by weight.

(3) The initial pH. of the. polymerization reaction mixture must be, above 4 and must be permitted to fall map}; not higher than 6 before completion of the reaction.

(4) The polymerization "is continued until the polymer content has reached at least 20% by weight but not morethan about 40 If any one of the above four requirements-is not met in the polymerization procedure the resulting product will-not be a stable emulsion which form water-resistant; films. Qndrying. For example, the. dispersing: agent. isfaz par-. tially hydrolyzed. grade of polyvinyl alcohohthe resulting emulsion will not formwater-resistant films, regardless; of the regulation of'-mnnomer..- content during polymerization. If the. monomer content of. the reaction mixture initially exceeds.. 5% or; exceeds 31%. when thepolymer content; is above 20% during the polymerization reaction, the water resistance of films cast from t'heiresulting' product will lee-unsatisfactory.

Proceeding in accordance: 'vvithjthev abovestated four essential requirements, dispersionsiwhich. produce films not redispersiblein water. can. bev made without the addition of the high molecular weight alcohol. However, without the; addition of a high molecular weight. alcohol, *e.: g.,. lauryl alcohol, before the polymerization. is more than'50% complete, the emulsion. will nothave a high dilution stability. The dilution stability can be evaluatedby means or the 6% Solids: Dilution Settling Test described above. shownby the above examples, the addition of the high molecular weight alcohol markedly re-i ducestheamount of solids settled out 24 hours: from an emulsion diluted to 6% polymer con-- centration; Ingeneral the effect of thelauryl alcohol or other suitable: high molecular'w'ei ght alcohol is to decrease the particle'siz'e of the dispersed polymer and also to decrease the amount of agglomerates; This effect 'is' demon strated by the above described Percent Screen Test.

In place of:lauryl: alcohol, I may employ any monohydric; primary alcohol containing 8' tpZZO' carbon atom in the molecule, either straight: chain or branched chain, provided that the molecule contains at least onechain of, not less'thaii 8 carbon atoms. The alcohol maybe saturated or. monoolefinio; that is, itgmay have not pr fer to employ saturated alcohols, as the monoolefiriic alcohols tend to inhibit polymerization, require ing the. employment of large amounts ofipol g merization catalyst. Thus, the suitable alcohols may be expressed by the generic formulaCd-IQOH;

11 where :c=8 to 20 and y=2m+1 or Zx-l, with the proviso that the radical CxHy contains a straight-chain of not less than 8 carbon atoms. Examples of such alcohols are:

CsHnOH n-Octyl alcohol CioHziOH n-Decyl alcohol CmHasOI-I Lauryl alcohol C18H37OH n-Octadecyl alcohol CH3 (CH2) 1CH=CH (CH2) aOH Oleyl alcohol CH3 (CH2) 12CH2OI-I Myristic alcohol CreHacOI-I Cetyl alcohol C17H35OH n-Heptadecylalcohol z)aCH( 2)a 2)aCCHCH1OH H: CH3 H: CH3

Phytol (3,7,11,15, -tetramethyl-2-hexadecen-1-ol) The optimum chain length for the high molecular weight alcohol is C12 and lauryl alcohol is the'preferred species. In the homologous series of straight-chain, saturated primary alcohols CnH21l+1OH, where n:8 to 20, the best results are obtained with lauryl alcohol (C12H25OH) and the above described beneficial results decrease as the number of carbon atoms become either greater or less than 12.

Mixtures of the alcohols may be used in place of a pure .alcohol. A preferred mixture is a proprietary composition known as Lorol which is a somewhat impure mixture of high molecular weight alcohols containing around 90% of lauryl alcohol.

Control of monomer content of the polymerization reaction mixture is an important and essential feature of my process. During the reaction, the monomer content, regulated by the rate of addition of monomer, must not exceed by weight of the reaction mixture when the polymer content is 20% by weight or less and must not exceed 3% by weight when the polymer content exceeds 20%. Preferably, I begin the reaction with around 1 to 1.5% of vinyl acetate in the emulsion and maintain the vinyl acetate content at 1.5 to 3% during most of the reaction. By employing a nitrogen atmosphere to exclude air as described below, I may maintain the vinyl acetate monomer content at not over about 0.4%, which gives the best product at reasonably low catalyst consumption. If desired, the monomer content may be maintained as low as 0.1%. To control the monomer concentration, the vinyl acetate is added substantially at the rate of its polymerization and catalyst is added continuously or intermittently as required to maintain reaction.

It is desirable to exclude air from the reaction mixture, as molecular oxygen has an inhibitory effect on the polymerization. Preferably, the air is excluded by operating in a closed reactor equipped with a reflux condenser and maintaining an atmosphere of vinyl acetate vapor over the reaction mixture. Alternatively, the reactor free space may be filled with an oxygenfree, inert gas such as nitrogen.

In practicing my invention, for the best results solve in cold water, I generally heat and stir amixture of the polyvinyl alcohol and water at 70 to 100 C. until substantially complete solution is obtained.

It is essential that the pH of the polymerization reaction mixture initially be above 4 and I prefer an initial pH of around 6 to 8. To insure a reasonably high pH I generally prefer to add a mild alkaline buffer such as sodium bicarbonate, disodium phosphate, sodium acetate, or the like. If the mixture initially contains acetic acid, it may be neutralized by adding the above alkali or a stronger alkali such as sodium hydroxide, sodium carbonate or the like. As the polymerization proceeds, the pH of the reaction mixture generally falls, due to formation of acetic acid, caused by hydrolysis of part of the vinyl acetate monomer. Preferably, the initial pH is so adjusted (e. g., to pH of 6 to 8) so that the final pH is above 4. However a good product may be obtained at a final pH below 4, provided that during the greater part of the reaction the pH is above 4. When a mild alkaline buffer such as sodium bicarbonate or disodium phosphate is used to adjust the initial pH, I prefer to add the buffer to the water before dissolving the polyvinyl alcohol therein.

If the initial pH is below 4, the resulting emulsion -produces water dispersible films. Low initial pH also tends to cause undue thickening of the emulsion, increase in particle size of the dispersed polymer, aggregation of particles and coagulation.

The polymerization temperature is not particularly critical and temperatures conventionally employed for polymerizing vinyl acetate with peroxide catalysts are suitable, e. g., from 50 to 90 C. I generally prefer to maintain the reaction mixture at reflux temperature, e. g., at to C. In operating at lower temperatures without refluxing, I prefer to maintain a nitrogen atmosphere in the reactor to exclude air.

The emulsions prepared as described herein are aqueous dispersions of solid polyvinyl acetate having improved characteristics. Films made by drying these emulsions at 20 to 25 C. or higher are substantially insoluble (i. e., not redispersible) in water at any temperature. These emulsions are further characterized by unusually small particle size of the polyvinyl acetate, high stability, both in concentrated and diluted forms, and relative freedom from agglomerates. The emulsions are useful for a variety of purposes, particularly for coating solid surfaces, and as adhesives. For such purposes the emulsions may be used per se or in combination with other ingredients such as pigments, extenders, fillers, plasticizers, colorants and the like.

I claim:

1. The process which comprises dispersing vinyl acetate monomer in a 2 to 10% by weight aqueous solution of a hydrophilic dispersing agent which is a polyhydroxy, polymeric, filmforming substance substantially insoluble in water at temperatures below 50 C. but soluble in water at a temperature not lower than 50 C. to form a dispersion containing not more than 5% by weight of said monomer, subjecting said dispersion to polymerization in the presence of a peroxygen type catalyst, while dispersing therein further quantities of said monomer so as to maintain a monomer concentration not greater than by weight when the polymer concentration is not over 20% by weight and not greater than 3% by weight when the polymer content has exceeded 20% by weight, continuing as above until the polymer content has reached 20 to 40% by weight, controlling the pH of the polymerization reaction mixture so that it is initially not less than 4 and finally not greater than 6 and adding to the reaction mixture before polymerization is 50% complete a primary, aliphatic alcohol having at least one chain of carbon atoms not less than 8 carbon atoms in length and corresponding to the formula CIHyO'H, where ;c:8 to 20 and 11: one of the values selected from the group consisting of 2a:+1 and 2112-1, in amount equal to 0.1 to 5% by weight of the total vinyl acetate polymerized, the concentration of said dispersing agent being sufiicient to form a stable emulsion of the resulting polyvinyl acetate.

2. The process which comprises dispersing vinyl acetate monomer in a 2 to 10% by weight aqueous solution of a hydrophilic dispersing agent which is a polyhydroxy, polymeric, filmforming substance substantially insoluble in water at temperatures below 50 C. but soluble in water at a temperature not lower than 50 C. to form a dispersion containing not more than 5% by weight of said monomer, subjecting said dispersion to polymerization in the presence of a peroxygen type catalyst, while dispersing therein further quantities of said monomer so as to maintain a monomer concentration not greater than 5% by weight when the polymer concentration is not over by weight and not greater than 3% by weight when the polymer content has exceeded 20% by weight, continuing as above until the polymer content has reached 20 to 40% by weight, controlling the pH of the polymerization reaction mixture so that it is initially not less than 4 and finally not greater than 6 and adding to the reaction mixture before polymerization is 50% complete a straight-chain alcohol having the formula C1LH21L+1OH where 11:8 to 20, in amount equal to 0.1 to 5% by weight of the total vinyl acetate polymerized, the concentration of said dispersing agent being sufficient to form a stable emulsion of the resulting polyvinyl acetate.

3. The process which comprises dispersing vinyl acetate monomer in a 2 to 10% by weight aqueous solution of a completely saponified grade of polyvinyl alcohol in concentration of said monomer equal to 0.1 to 5% by weight, subjecting the resulting dispersion to polymerization in the presence of peroxygen type polymerization catalyst and adding and dispersing therein further amounts of said monomer in such quantities that the monomer concentration never exceeds a certain value, depending upon the concentration of dispersed polymer, as follows: not over 5% when the polymer concentration is not over 20% by weight; not over 3% when the polymer concentration is more than 20% by weight; continuing said addition of monomer until the resulting dispersion contains 20 to 40% by weight of polymer, controlling the pH of the polymerization reaction mixture so that it is initially not less than 4 and finally not more than 6 and adding to the reaction mixture before polymerization is 50% complete a straight-chain alcohol having the formula Cnl-hnHOl-I where 11:8 to 20, in amount equal to 0.1 to 1% by weight of total vinyl acetate polymerized, the

concentration of said polyvinyl alcohol being sufficient to form a stable emulsion of the resulting polyvinyl acetate.

4. The process according to claim 3 in which the polymerization catalyst is an activated peroxide type and the straight-chain alcohol is lauryl alcohol.

5. The process according to claim 4 in which the polymerization catalyst comprises hydrogen peroxide and a sulfoxylate, separately added to the reaction mixture.

6. The process according to claim 5 in which the monomer content is regulated not to exceed 3% by weight throughout the polymerization reaction.

'7. The process according to claim 6 in which the aqueous solution of polyvinyl alcohol is prepared by dispersing and heating the polyvinyl alcohol in Water containing sufiicient alkaline salt to adjust the pH to above 4.

8. The process according to claim 7 in which the alkaline salt is sodium bicarbonate and the pH is adjusted to 6 to 8.

NORRIS TURNBULL. I

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,245,040 Marks June 10, 1941 2,317,138 Fletcher Apr. 20, 1943 2,508,341 Wilson May 16, 1950 2,535,189 Benson et al. Dec. 26, 1950 

1. THE PROCESS WHICH COMPRISES DISPERSING VINYL ACETATE MONOMER IN A 2 TO 10% BY WEIGHT AQUEOUS SOLUTION OF A HYDROPHILIC DISPERSING AGENT WHICH IS A POLYHYDROXY, POLYMERIC, FILMFORMING SUBSTANCE SUBSTANTIALLY INSOLUBLE IN WATER AT TEMPERATURES BELOW 50* C. BUT SOLUBLE IN WATER AT A TEMPERATURE NOT LOWER THAN 50* C. TO FORM A DISPERSION CONTAINING NOT MORE THAN 5% BY WEIGHT OF SAID MONOMER, SUBJECTING SAID DISPERSION TO POLYMERIZATION IN THE PRESENCE OF A PEROXYGEN TYPE CATALYST, WHILE DISPERSING THEREIN FURTHER QUANTITIES OF SAID MONOMER SO AS TO MAINTAIN A MONOMER CONCENTRATION NOT GREATER THAN 5% BY WEIGHT WHEN THE POLYMER CONCENTRATION IS NOT OVER 20% WEIGHT NAD NOT GREATER THAN 3% BY WEIGHT WHEN THE POLYMER CONTENT HAS EXCEEDED 20% BY WEIGHT, CONTINUING AS ABOVE UNTIL THE POLYMER CONTENT HAS REACHED 20 TO 40% BY WEIGHT, CONTROLLING THE PH OF THE POLYMERIZATION REACTION MIXTURE SO THAT IT IS INITIALLY NOT LESS THAN 4 AND FINALLY NOT GREATER THAN 6 AND ADDING TO THE REACTION MIXTURE BEFORE POLYMERIZATION IS 50% COMPLETE A PRIMARY, ALIPHATIC ALCOHOL HAVING AT LEAST ONE CHAIN OF CARBON ATOMS NOT LESS THAN 8 CARBON ATOMS IN LENGTH AND CORRESPONDING TO THE FORMULA CXHYOH, WHERE X=8 TO 20 AND Y= ONE OF THE VALUES SELECTED FROM THE GROUP CONSISTING OF 2X+1 AND 2X-1, IN AMOUNT EQUAL TO 0.1 TO 5% BY WEIGHT OF THE TOTAL VINYL ACETATE POLYMERIZED, THE CONCENTRATION OF SAID DISPERSING AGENT BEING SUFFICIENT TO FORM A STABLE EMULSION OF THE RESULTING POLYVINYL ACETATE. 